Control circuits



Aug. 14, 1956 w, FEW ET AL 2,759,139

CONTROL CIRCUITS Original Filed Aug. .12, 1948 3 Sheets-Sheet 1INVENTORS WILL\AM FEWAND JOHN D.SAUTETZ.

ATTORAEYT Aug. 14, 1956 w. FEW ET AL 2,759,139

CONTROL CIRCUITS Original Filed Aug. 12, 1948 3 Sheets-Sheet 2INVENTORS.

F 3 WILLIAMv FEW AND 1 BY JOHN D. SAUTEE.

ATTORNEY g 1956 w. FEW ET AL 2,759,139

CONTROL CIRCUITS Original Filed Aug. 12, 1948 3 SheetsSheet 3 INVENTORS.Wl LLlA M FEW AND JOHN D. SAUTER.

ATTORJVZ'Y United States Patent CONTROL CIRCUITS William Few and John D.Sauter, Cleveland Heights, Ohio, assrgnors to The Clark ControllerCompany, Cleveland, 01110, a corporation of Ohio 43,787, 2,664,529,dated December 29, 1953. application April 6, 1953, Serial No.

6 Claims. (Cl. 321-16l This application is a division of our co-pendingapplication, Serial Number 43,787, filed August 12, 1948, now Patent No.2,664,529. Our invention relates to electric curcuits for speed andcurrent control.

An object of the invention is to obtain continuous variation ininfinitesimal increments of an electric current in response tovariations in position of a movable member. More specifically, it is anobject to obtain such current variation in a direct-current circuit suchas, for example, the direct-current winding of a saturable reactor.Furthermore, it is an object to render a saturable reactor, responsivecontinuously in infinitesimal increments to variations in position of amechanical member such as the dancer arm of a multiple-block wiredrawing machine.

Another object of the invention is to avoid hunting in the rotation ofmotor driven units such as the capstans of a multiple-block wire drawingmachine and to obtain infinitesimal increments in the adjustment ofspeed of successive capstans, so that the dancer arms carrying loops ofwire from one die to the next capstan may remain in a given position,without the necessity for constant working back and forth to obtain anaverage speed appropriate to the speed with which the next capstan drawsthe wire through the di Still another object of the invention is toobtain very rapid adjustment in the speed of motor driven unit such asthe capstans appropriate to the speed of the succeeding motor drivenunits such as capstans while avoiding huntmg.

Other and further objects, features and advantages of the invention willbecome apparent as the description proceeds.

In carrying out our invention in accordance with an improved embodimentthereof, we utilize manual control of the speed of the motor driving thelast capstan of the series of multiple-block wire drawing machine, andthe speeds of the motors driving the preceding capstans areautomatically adjusted to the proper speed for the speed at which thelast capstan draws the wire through the final die. Separate motors areemployed for driving each capstan, and either a constant voltage,direct-current source may be employed for driving the motors or avariable voltage generator may be provided for energizing all of thecapstan motors.

The motors are preferably compound wound directcurrent motors havingseries fields and also having shunt fields. Conventional pivoted dancerarms, upon which are mounted pulleys for carrying the loops of wire fromone capstan to the succeeding die, are provided for controlling theshunt field excitation of the preceding capstan motor at such a speedthat the length of the loop neither increases nor decreases and thesuccessive capstan speeds are proportional to the draft of the diebetween successive capstans. In order to obtain continuous speedvariations with infinitesimal increments, to increase the reliability ofspeed control and the rapidity with which adjustments may be made, aswell as to increase the sturdi- 2,759,139 Patented Aug. 14, 1956 acesand life of the apparatus and avoid the difliculty of maintenance ofcontacts and rheostats, we provide electronic current control for theshunt fields of the motors.

In the preferred arrangement some of the field current is supplied froma constant potential source through a manually adjustable rheostat,which is ordinarily left in a fixed position, after the suitableadjustment has been ascertained and the adjustment of variation in fieldcurrent is provided by a phase-responsive rectifier of the gas or vapordischarge type, commonly referred to as a thyratron type of rectifier.The phase control of the rectifier is made responsive to the angularposition of the dancer arms, each dancer arm being arranged to controlthe field current of the motor driving the preceding capstan. The phasecontrol may be obtained by a suitable phase shifter, such as a bridgetype phase adjustor of the resistance-reactance type, for example, inwhich the magnitude of one of the electrical dimensions is adjusted forchanging the phase. Preferably a saturable reactor is utilized as thereactance arm of the phase adjustor and the phase adjustment isaccomplished by varying the direct-current flow through the directcurrent winding of the saturable reactor. If desired, however, a movablearmature adjustable reactor may be employed in which the armature ismechanically linked to the dancer arm.

Where a saturable reactor type of phase adjustor is employed, anelectronic type of current adjustor is preferable. We have found thatprecise, reliable and rapid adjustment of the direct-current in asaturable reactor responsive to movement of a movable member, such asthe dancer arm, is preferably obtained by means of a vacuum tube type ofrectifier with anticipating or antihnnt circuits incorporated inthedegenerative bias thereof, and having control grids excited by thesecondary winding of a variable ratio transformer, the ratio of which isdetermined by the relative angular positions of the primary andsecondary windings. For example a synchronous generator of the type soldas a Selsyn motor or generator may be employed in which the rotor ismechanically linked to the dancer arm of the wire block machine. Inorder that sensitivity adjustment and adjustment of the zero position ofthe dancer arm may be obtained electrically without requiring any changein mechanical linkage, a bridge type of connection is preferablyinterposed between the secondary winding of the variable ratiotransformer and the grid circuit of the vacuum tube rectifier. Suchbridge circuit includes a sensitivity adjustment potentiometer and aposition adjustment potentiometer and a position adjustmentpotentiometer, as will be described more in detail hereinafter. Controlcircuits are also so arranged that full hold is automatically applied tothe capstan motor when the machine is started, independent of theposition of the dancer arms.

A better understanding of the invention will be afforded by thefollowing detailed description considered in conjunction with theaccompanying drawing, in which Fig. 1 is a schematic diagram of amultiple-motor multiple capstan wire block machine in which the dancerarms are arranged for controlling motor speed in accordance with ourinvention;

Fig. 2 is a circuit diagram of one form of electrical system which maybe employed for driving the motors shown in Fig. 1 with details of theelectronic field control circuits omitted for clarity in the drawing;

Fig. 3 is a detailed circuit diagram of the field current controlcircuit for one of the capstan driving motors other than the lastcapstan driving motor in accordance with an embodiment of our invention;

Figs. 4a, 4b, 4c and 4d are graphs, which illustrate the principle ofoperation of the vapor discharge type phase-responsivecurrent-controlling rectifiers indicated in Fig. 2 and shown moreclearly in Fig. 3, and which illustrate the operation for differentpositions of the dancer arm and different operating conditions of thewire block machine; and

Figs. 5a, 5b, 5c, 5d, and 5e are graphs, which illus trate the principleof operation of the vacuum tube type direct-current regulator shown inFig. 3 for regulating the magnitude of the current in the direct-currentwinding of the saturable reactor, and which illustrate the operation fordifferent positions of the dancer arm and different positions of themechanism for adjusting the control voltage of the current regulator.

Like reference characters are utilized throughout the drawing todesignate like parts.

Wire block machines have been produced having dancer arms which operatesliding-contact field resistors for adjusting the speeds of capstanmotors to maintain as nearly as possible constant lengths of the wireloop between one capstan and the succeeding die. Such arrangementshaving three or four capstan motors with automatically controlled speedshave been built and maximum wire speeds as high as one thousand feet(1,000 ft.) per minute have been obtained. It is an object of ourinvention not only to enable the speed of wire drawing to be greatlyincreased to about three thousand feet (3,000 ft.) per minute, forexample, but also to enable wire drawing to be accom plished efiicientlyand without damage or breakage in connection with materials which aremore diificult to draw, such as very hard wire, wire rope or stainlesssteel wire and the like. Furthermore, it is an object to facilitateincreasing the amount of drafts which may be obtained with reliableoperation. We may, for example, employ six or more separately controlledcapstan driving motors having their speeds automatically controlled inaccordance with our invention. For simplicity, however,

in Fig. 1 we have shown an arrangement with only three capstan motorswhich are automatically controlled and a finaldraw capstan motor whichis manually adjusted to the desired output speed. The three precedingcapstan motors illustrated adjust themselves automatically to the properspeeds for obtaining suitable operation of the machine in proportion tothe speed of the final draw capstan. The manner in which additionalnon-illustrated automatically controlled capstan motors and their fieldcontrols would be arranged will be apparent to those skilled in the art.

Referring to Fig. 1, we may, in accordance with frequent practice,employ a first capstan 11 having two different drums 12 and 13 so as toobtain a double draw through dies 14 and 15 in succession. ever, thesucceeding capstans 16 and 17 and 18 are driven by separate motors andeach follows a single die so that individual adjustment of the speed ofdraft through dies 19 and 20 and 21 may be obtained without slippage ofwire on any of the capstans. The capstans 11, 16 and 17 are driven bymotors 22, 23 and 24 respectively, each of which is provided withautomatic field control in accordance with our invention and the capstan18 is driven by a motor 25 having manual field control by which theoutput speed of the machine is determined.

A movable pulley carried by a spring-biased dancer arm is provided forcarrying a loop of wire between each capstan and the succeeding die.Thus between the capstan 11 and the die 19 there is a movable pulley 31mounted on a dancer arm 32 for carrying a loop of wire 33 passing fromthe drum 13 of the capstan 11 around the pulley 31 to the die 19. Forkeeping the wire loop 33 taut, a spring 26 is provided for the arm 32.The dancer arm 32 is pivoted at 34 upon a shaft 35 which is connected orotherwise linked to the rotor, not shown in Fig. l, of an adjustableratio transformer such as a Selsyn 36 for example. Similar spring-biaseddancer arms 37 and 38 mechanically connected to Selsyns 41 and 42 areprovided between the capstan 16 and the die 20 and between the capstan17 and the die 21.

Prefer-ably, how- For energizing the motors 22, 23, 24 and 25 a constantpotential, direct-current source or, if desired, a variable voltagesystem is utilized having a separate variable voltage generator forenergizing all the motors of the block. For the sake of illustration,the latter type of system has been represented in Fig. 2, as shown, by amain generator 51 supplying the motors 22, 23, 24 and 25 through powerconductors 52 and 53. A source of substantially constant-potentialexciting current is provided having a positive terminal 54 and anegative terminal 55. The main generator 51 has a field winding 56energized from the direct-current source 54 and through suitable fieldadjusting rheostats or potentiometers, such as the potentiometer 57 asindicated. The same direct-current source 54-55 may be employed, asshown, for providing a portion of the shunt field current for the motors22, 23, 24 and 25. These motors may, if desired, be of the compoundwound type having series fields 58. The motors 22, 23, 24 and 25 alsohave potential field windings 59, 61, 62 and 63, respectively, which maybe called shunt field windings by analogy to the conventional connectionfor compound wound motors. The motor 25, having manual speed adjustment,has its field winding 63 supplied entirely from the direct-currentsource '5455 through a manually operated field rheostat 64 of theconventional type. The automatically controlled motors 22, 23 and 24have their field windings 59, 61 and 62 connected to the source 5455 inseries with manually operated rheostats 65, 66 and 67, respectively.These rheostats 65, 66 and 67 however, are normally left in a fixedposition during operation, and for obtaining field control,supplementary current supply sources 68, 69 and 70 are provided. Thesesources 68, 69 and 70 are of the electronic or vapor-discharge type andare indicated only fragmentarily in Fig. 2. Each of the current supplysources 63, 69 and 70, as shown, has positive and negative outputconductors 71 and 72 connected across the motor shunt field winding andpreferably a voltage-limiting discharge resistor 73 is also connectedacross the field winding.

Each of the discharge resistors 73 is composed of a material with theproperty of having a negative voltage coeflicient of resistance, so thatthe voltage can rise relatively little above the predetermined valuedetermined by the dimensions and arrangement of the resistor. Theseresistors may consist of so-called Thyrite, or material having thecomposition described in Patent No. 1,822,742, McEachron.

Since the field current controlling devices 68, 69 and 70 are similar, asingle detailed drawing of the complete circuit of one of them is shownin Fig. 3. They are all energized from a source of alternating current74, and, if desired, a multiple-secondary transformer having a commoncore and a primary winding 75 may be provided with separate secondarywindings 76, 77 and 78 for the regulators 68, 63 and 70 respectively. Asillustrated in Fig. 3 the regulator 70 comprises, in combination withthe transformer having the secondary winding 78, a pair of electricdischarge devices 79 and 80, an excitation phase adjusting circuit 82including a saturable core reactor 83, and a saturation controllingcircuit 84 responsive to the angular position of the dancer arm 38. Thedischarge devices 79 and are preferably of the gas or vapor dischargetype in which current conductivity is maintained, so long as positiveanode potential remains, once the grid or control electrode potentialhas been raised to a predetermined value, regardless of subsequentfluctuations in the grid potential. Such discharge devices are commonlyreferred to as thyratron tubes and the term thyratron will be usedthroughout the description and claims to refer to this type of electricdischarge device or current controlling device. The thyratrons 7? and 80comprise envelopes containing suitable gas or vapor, and enclosingplates or anodes 85 and 86, cathodes 87 and 88 (heater current sourcesbeing omitted for simplicity), and control electrodes or grids 89 and 90re- Spectively. In order that full wave rectification may be obtained apair of thyratrons 79 and 80 is employed but our lnvention is notlimited thereto.

In the arrangement illustrated, the anodes and 86 are connected throughsuitable anode resistors 91 and 92 to opposite ends of the transformerwinding 78. The cathodes 87 and 88 are connected to the positive inputconductor 71 of the field winding 62, and the negative input conductor72 of the field Winding 62 is connected to a genter tap 93 of thetransformer secondary windmg 7 The phase adjuster 82 has a pair ofvariable phase output conductors 94 and 95 connected to the controlelectrodes 89 and 90 through current-limiting resistors 96.

The phase adjustor 82 in the form illustrated comprises a triangularbridge having a voltage supply arm 97, a resistance arm 98, a reactancearm 99 and a cross arm 101. The input voltage supply arm 97 constitutesa secondary winding of a transformer having a primary winding 102supplied with voltage in the same phase as the voltage 74. For thepurpose of circuit isolation, preferably a secondary winding 103 isprovided on the core of the transformer 75 for energizing the phaseshifter primary winding 102. For the sake of circuit isolation, also,the cross arm 101 takes the form of transformers 104 having primarywindings 105 connected in parallel, the parallel group being connectedat one end to a center tap 106 of the transformer winding 97 and at theother end to a common terminal 107 of the resistor arm 98 and thereactance arm 99. The transformers 104 have secondary windings 108 and109 connected in the control electrode circuits respectively of thethyratrons 79 and 80, through the conductors 94 and 95, and a neutralconductor 71a.

The saturablc reactor 83 comprises a pair of parallel connectedalternating-current windings forming the reactance arm 99 and adirect-current winding 111. As will be understood by those skilled inthe art, such saturable reactors commonly comprise three-legged coreswith a direct-current winding wound on a center core, or an equivalentarrangement with the alternating-current windings connected so as toavoid inducing high voltage in the direct-current winding.

The saturating current controller 84 comprises a pair of high vacuumtubes 112 and 113 having control electrodes or grids such as triodes6SN7G, e. g., with a plate or anode supply such as a transformer 114,and having control voltage supplied by the variable ratio transformer orSelsyn 42, energized by the same transformer 114, so as to preservein-phase or out-of-p'hase relationship between the anodes and the gridsof the tubes 112 and 113.

The tubes 112 and 113 are provided with a cathode bias resistor 115shunted by a smoothing condenser 116. The capacity of the condenser 116,however, is sufficiently small so that appreciable degenerative efiectis obtained. Preferably, anticipating circuits are interposed in thecoupling of the control voltage to the control grids, in order to assistfurther in avoiding hunting. For example, a difierentiating circuit maybe provided comprising a potentiometer 117 and a condenser 118 connectedin series across the cathode resistor 115 and an integrating circuit maybe provided comprising a condenser 119 and a potentiometer 120 connectedin series between the cathode terminal 122 and a tap or adjustablecontact 123 of the potentiometer 117. The control voltage may beinterposed between the tap or adjustable contact 124 of thepotentiometer 120 and the control grids of the tubes 112 and 113, butpreferably the control voltage is supplied through a bridge arrangement125 in order that sensitivity adjustment and position adjustment may beprovided.

The tubes 112 and 113 contain anodes 126 and 127, control electrodes 128and 129 and cathodes 131 and 132 respectively. The anodes 126 and 127are connected to opposite ends of a winding 133 forming a secondarywinding in the transformer 114, the primary winding 134 6 of which maybe energized from the winding 103 in com men with the winding 102 of thephase shifting bridge 82. The direct-current winding 111 of thesaturable reactor 83 is connected between the center tap 135 of theplate transformer winding 133 and the negative end terminal 136 of thecathode resistor 115.

The bridge circuit 125 comprises a supply winding 137 which is anothersecondary winding of the transformer 113 having a center tap 138, and aposition adjusting potentiometer 139 connected across the winding 137,preferably with resistors 141 and 142 connected in series with bothterminals. The cross arm of the bridge 125 comprises a pair of parallelconnected primary transformer windings 143 and 144 connected between anadjustable tap 145 of the potentiometer 139 and an adjustable tap 146 ofa sensitivity-adjustment potentiometer 147 having an end terminal 148connected to the center tap 138 of the winding 137. The windings 143 and144 constitute primary windings of transformers 148 and 149 havingsecondary windings 151 and 152, respectively. The secondary windings 151and 152 have a common terminal 153 connected to the adjustable tap 124of the potentiometer 120. The free ends of the transformer windings 151and 152 are connected through current limiting resistors 154 and 155 tothe control electrodes or grids 128 and 129 of the tubes 112 and 113respectively.

The variable ratio transformer 42 in the form illustrated comprises analternating-current dynamo electric machine having windings both on thestator and the rotor. To avoid unnecessary stocking of special parts, adevice with a three-phase stator may be employed having threeY-connected coils for exampie. Only two of the Y-connected coils, 156and 157, are shown in order to avoid confusion in the drawing. The rotorin the arrangement illustrated comprises a winding 159. Since the deviceis operated single phase, only one or two of the stator windings need beemployed, and as illustrated, the coils 156 and 157 are connected inseries across the sensitivity adjustment potentiometer 147 and the rotorwinding 159 is connected across the input alternating-current supply,viz., the transformer secondary winding 137. As shown, the pivoted arm38 or dancer arm is mechanically con nected to the rotor 159. Theinvention obviously is not limited to the specific type of variableratio transformer employed nor to the connection of the voltage input tothe rotor and the voltage output terminals to the stator instead of viceversa.

As will be explained more in detail hereinafter, when the minimum orzero voltage appears across the primary windings 143 or 144 of thecalibrating bridge 125, current fiows in the direct-current winding 111of the saturable reactor 83 and the phase responsive rectifiers '79 and80 carry maximum current so as to supply full field to the motor, thusobtaining maximum torque or minimum speed of the motor and facilitatingstarting. This circumstance is taken advantage of to provide automaticsafety arrange ments for assuring that all motors of the multiple-blockwire drawing machine will have maximum torque and a minimum speed whenthe apparatus is started up. Accordingly, a pair of normally closedcontacts 161 is connected across transformer windings 143 and 144 of thecalibrating bridge 125. The contacts 161 constitute stationary contactscooperating with a movable contact 162 carried by a plunger 163 ininductive relation to a winding 164 connected to a suitable powercircuit, for example, across the armature brushes of the motor inquestion, viz., the motor 24. (See Fig. 2.) Similar normally closedcontacts are provided for the motors 22 and 23, but have been omittedfrom the description and drawing for the sake of simplicity.

A conventional arrangement, not shown, is likewise provided for themotor 25 to shunt out its manual field control resistor 64 when theapparatus is started.

Referring to Fig. 1, the first operation in starting the machine is, ofcourse, starting a tapered end of wire through the dies 14, 15, etc.This operation is conventional and need not be further described. Afterthe wire has been passed around the capstans and the movable pulleys 31,and upon supplying power through the armature, the normally closedcontacts such as the contacts 161 are initially closed. This gives themotors maximum field and maximum torque. As soon as the motors have comeup to speed sufiiciently to produce a predetermined back voltage acrossthe armature, the winding 164 is energized opening the contacts 161 andthe operation of each of the automatically controlled motors 22, 23 and24 proceeds under the control of the electronic field control circuits,such as that for the motor 24 illustrated in Fig. 3.

Referring to Fig. 1, if the capstan 17 is not rotating rapidly enough inrelation to the capstan 18, the wire is being drawn into the die 21 morerapidly than it leaves the capstan 17. In other Words the wire or otherfilar element in the rear is not being supplied rapidly enough inrelation to the portion thereof in advance. Accordingly,

the wire loop 33 is being shortened and the dancer arm 38 is drawndownward (with respect to the position illustrated in Fig. 1). Thisrotates the rotor 159 of the Selsyn type variable ratio transformer 42toward the position in which the voltage output of the windings 156 and157 is greater; accordingly, a greater voltage appears in thepotentiometer 147. The voltage supplied to the primary windings 143 and144 of the transformers 148 and 149 is increased and a greater voltageappears on the control electrodes 128 and 129 of the tubes 112 and 113.This decreases the average potential of the control grids, for thefollowing reason. The characteristics of the tubes 112 and 113 are suchthat the grids cannot rise above cathode potential during positive halfcycles of the control grid voltage, and accordingly only the negativehalf cycles of control grid voltage are ettective. The output of thetubes 112 and 113 is decreased with decreasing average grid potential,thus decreasing the flow of directcurrent through winding 111 of thesaturable reactor 83. This in turn increases the reaetance of thiswinding and increases the phase shift produced by the phase adjustingbridge 82.

Thereupon the anodes and the control grids of the thyratron tubes 79 and89 are brought out of phase, the current output thereof is decreased,the field strength of the motor 24 is decreased and the speed increases.This enables the capstan 17 to supply wire at a greater speed andenables the wire loop 33 to increase in length again until the dancerarm 38 has found an angular position at which the ratio of the speed ofthe capstan 17 to the speed of the capstan 18 equals the reciprocal ofthe draft through the wire die 21.

in a similar manner the speed of the capstan 16 is automaticallyadjusted to take the proper relation to the speed of the capstan 17 andthe speed of the capstan 11 is adjusted to take proper relation to thatof the capstan 16. Excessive change speed and overshoot is avoided byreason of the anti-hunt or anticipating circuits in the grid controlThus, if the arm 38 should be moved abruptly as a esult of an abruptchange in the manual setting of the motor 25 or for another reason, adegenerative or opposing change in control voltage of the grids 128 and129 will be produced as a result of the change in current fiow throughthe partially degenerative cathode resistor 115 applied todifferentiating circuit 117118, partially moditied by the integratingcircuit 11912ti. These circuits are so connected that they produce anopposing effect which increases with abruptness of the actual change andholds back tl :3 speed correction of the motor in order to enableconditions to stabilize.

The manner in which the phase responsive reetifiers 79 and function tocontrol field current in response to variations in phase of the grids isillustrated in Figs. 4a to 4d, wherein the sine wave curves 165illustrate the voltage applied to the anode of one of the tubes, forexample the anode 85 of the tube 79, by the transformer winding 78. Thedotted sine wave 166 represents the voltage applied to the control grid89 from the phase shifting bridge network 82 when the current flowin gin the winding 111 of the saturable reactor 33 is such as to balance thereaetance of the Winding $9 against the resistance of the winding 98 andproduce a quadrature reiationship between the grid voltage 166 and theanode voltage .165. As will be understood by those skilled in the art,the current flow in the tube 79 is extinguished whenever the anodevoltage 165 falls below zero. The flow of current can be resumed againwhen the anode voltage 165 rises above zero only when the grid potentialis above a predetermined value, ordinarily slightly below but quiteclose to zero and depending upon the amplitude of the anode voltage.

Thus in the case illustrated in Fig. 4a, the control grid voltage 166does not reach the ignition voltage until at or very nearly at the timecorrespondin to one-quarter wave length after the beginning of the wave165. Thereupon the tube 79 becomes conducting and remains conducting, asillustrated by the shaded portion of the sine wave 167, until the wave165 falls to zero. If the control. grid voltage had lagged less behindthe anode voltage, as illustrated by the dotted since wave 168 in Fig.4b, the tube would have become conductive sooner, as illustrated by theshaded portion 169. Since the tube is conducting for a longer period oftime, the average current flow is greater and the average direct-currentflowing through the motor field is greater, resulting in lower motorspeed and resulting in degenerative braking if the motor has beentraveling at a speed greater than the running-light speed which would beproduced by the new field adjustment illustrated in Fig. 4!).

On the other hand, if the control grid voltage is considered to lagconsiderably behind the anode voltage, as illustrated by the dotted sinewave 171 in Fig. 4d, the tube conducts current fora relatively shortportion of the cycle represented by the shaded area 172, and the averagefield current is reduced and the motor speed is increased. At starting,when the windings 143 and 144 are short-circuited by the normally closedcontacts 161, a maximum current flows through the tubes 112 and 113. Thecore of the saturable reactor 83 is so highly saturated that it hasnegligible reaetance so that the output voltage is very nearly in phasewith the input voltage, that is to say, the anode and the grid voltagesof the thyratron tubes are very nearly in phase, as illustrated in Fig.4c, and maximum current full field is produced as shown by the shadedarea 173.

In Fig. 5a the curve 176 represents the anode voltage applied by thetransformer winding 133 to one of the vacuum tubes, for example, thevacuum tube 112. The tube does not conduct current through the negativehalf cycles of anode voltage so that the potential of the grid duringsuch negative half cycles is immaterial. The grid voltage cannot riseabove cathode voltage during the positive half cycles of the anodevoltage because grid current would then start to flow, resulting involtage drop through the current limiting resistor 155. Accordingly, thecurrent output of the tube is determined by the amplitude of thenegative voltage applied to the control grid during the positive halfcycles of anode voltage. Such tubes conduct current in decreasing valueas the grid potential is reduced or the negative grid voltage is madegreater to a certain value called the cut-off value at which the currentflow becomes zero. Thus, as illustrated in Fig. 5!), when the voltageinput to the control grid 128 is substantially zero, as shown by thedotted line 177, a maximum anode current half cycle is produced. On theother hand, with progressively greater values of control grid voltagerepresented by increasingly largeamplitude sine waves 178, 179 and 180,progressively smaller values of anode current are caused to flow, as

9 represented by the progressively-smaller shaded areas 181, 182 and133.

The voltage output of the variable ratio transformer 42 is tapped oif bythe adjustment contact 146 of the potentiometer 147, of the calibratingbridge .125 shown in Fig. 3. Consequently, the amplitude of responseobtained by rotation of the rotor 159 depends upon the position of thetap 146. Accordingly, this potentiometer serves as the sensitivityadjustor.

The control grid voltage for the tubes 112 and 113 is taken from thetransformers 148 and 149 and these are connected in the bridge cross armbetween the center tap 138 of the supply winding 137 and the adjustabletap 145 of the posit-ion adjusting potentiometer 139. Therefore, themagnitude and phase of the voltage output of the variable ratiotransformer 42, required to produce zero voltage output from thewindings 151 and 152, depends upon the angular position of the tap 145.For example, if this is placed at such a position that its potentialequals the potential of the center tap 138, the voltage output of thewindings 151 and 152 will be zero when the rotor 159 is in apredetermined angular position with respect to the stator windings 156and 157. Rotation of the dancer arm 38 in a given direction will thenincrease the voltage and rotation of the dancer arm in the oppositedirection will also increase the voltage but in opposite phase relation.

If it is desired to set back the angular position of the dancer arm 38,which results in zero voltage output at the windings 151 and 152, thisis accomplished by moving the potentiometer adjustable tap 145 to theleft so as to increase the output potential of the windings 151 and 152with respect to the tap 148 of the potentiometer 147. Accordingly, it isthen necessary for the arm 38 to move back introducing an out-of-phasepotential neutralizing that produced by the arm 145 of the positionadjusting potentiometer 139 in order to obtain a zero output from thewindings 151 and 152. Likewise, moving the arm in the oppositedirection, viz., in the direction of the arrow 184, has the effect ofadvancing the position of the arm 138 at which a predetermined currentflow from the tubes 112 and 113 is obtained.

It will thus be observed that a fully electrical control is obtained andno mechanical adjustments whatsoever are required for adjusting theangular positions of the dancer arms at which they maintain the desiredspeed relation, nor for adjusting the angular movement of the dancerarms required to produce predetermined variations in speed, :as theseadjustments are accomplished electrically by the potentiometers 139 and147. Furthermore, the adjustment of the degree of sluggishness orquickness of response in the change of motor speed and the change inspeed of the draft of wire by the succeeding capstan, is accomplished byadjustment of the :anti hunt potentiom eter arms 123 and 124 to give thedesired degree of first and second order anticipation. In this mannerovershoot in the correction of speed, and, therefore, hunting areovercome. Since the control of motor speeds is fully automatic and maybe made to respond very rapidly without hunting, wire may be drawnsafely and reliably at very high rates of speed.

Certain embodiments of the invention and certain methods of operationembraced therein have been shown and particularly described for thepurpose of explaining the principle of operation of the invention andshowing its application, but it will be obvious to those skilled in theart that many modifications and variations are possible, and it isintended, therefore, to cover all such modifications and variations asfall within the scope of the invention which is defined in the appendedclaims.

I claim:

1. A circuit for controlling the strength of current through adirect-current winding comprising in combination with such winding, apair of alternating-current supply terminals, a vacuum-tube typedirect-current controller having an anode-cathode circuit connectedtosaid altennating-current terminals having control electrode :means, avariable ratio transformer having a rotor the position of whichdetermines the voltage ratio, said transformer having a secondarywinding connected to said control electrode means, a degenerativeresistor for said controller, an anti-hunt differentiating circuitinterposed between said variable ratio transformer secondary winding andthe control electrode means, and a conductor connecting saiddirect-current winding in series with the anodecathode circuit of saidcontroller.

2. A direct-current controller comprising in combination with a pair ofalternating-current input terminals a high vacuum tube circuit havinganode and cathode means connected in series with said terminals andhaving control electrode means, a variable ratio transformer havingrelatively movable primary and secondary windings, the primary windingsbeing energized in the same phase relation with said alternating-currentinput terminals, a coupling between the secondary winding and saidcontrol electrode means, a degenerative resistor in the cathodeconnection of said vacuum tube circuit, an antihunt differentiatingcircuit interposed in the coupling between said variable ratiotransformer secondary winding and the control electrode means, andterminals for connecting a direct-current device to be controlled inseries with said anode-cathode circuit.

3. A direct-current controller comprising in combination with a pair ofalternating-current input terminals a high vacuum tube circuit havinganode and cathode means connected in series with said terminals andhaving control electrode means, a variable ratio transformer havingrelatively movable primary and secondary windings, the primary windingsbeing energized in the same phase relation with said alternating-currentinput terminals, a coupling between the secondary winding and saidcontrol electrode means, a degenerative resistor in the cathodeconnection of said vacuum tube circuit, and terminals for connecting adirect-current device to be controlled in series with said anode-cathodecircuit.

4. A direct-current controller comprising in combination with a pair ofalternating-current input terminals a high vacuum tube circuit havinganode and cathode means connected in series with said terminals andhaving control electrode means, a variable ratio transformer havingrelatively movable primary and secondary windings, the primary windingsbeing energized in the same phase relation with said alternating-currentinput terminals, a coupling between the secondary winding and saidcontrol electrode means, a degenerative resistor in the cathodeconnection of said vacuum tube circuit, an antihunt differentiatingcircuit interposed in the coupling between said variable ratiotransformer secondary winding and the control electrode means, terminalsfor connecting a direct-current device to be controlled in series withsaid anode-cathode circuit, a sensitivity adjustment potentiometerinterposed between the secondary winding of the variable ratiotransformer and the control electrode coupling, and a positionadjustment potentiometer interposed in the input connections to saidprimary winding for adjusting the relative angular position of thewinding of the said variable ratio transformer at which minimumexcitation of the control electrode means is obtained.

5. A direct-current controller comprising in combination with a pair ofalternating-current input terminals a high vacuum tube circuit havinganode and cathode means connected in series with said terminals andhaving control electrode means, a variable ratio transformer havingrelatively movable primary and secondary windings, the primary windingsbeing energized in the same phase relation with said alternating-currentinput terminals, a coupling between the secondary winding and saidcontrol electrode means, terminals for connecting a direct-currentdevice to be controlled in series with said anode-cathode circuit, asensitivity adjustment potentiometer interposed between the secondarywinding of the variable ratio transformer and the control electrodecoupling, and a position adjustment potentiometer interposed in theinput connections to said primary winding for adjusting the relativeangular position of the winding of the said variable ratio transformerat which minimum excitation of the control electrode means is obtained.

6. A direct-current controller comprising in combination with a pair ofalternating-current input terminals a high vacuum tube circuit havinganode and cathode means connected in series with said terminals andhaving relatively movable primary and secondary windings, the primarywindings being energized in the same phase relation with saidalternating-current input terminals, a coupling between the secondarywinding and said control electrode means, an anti-hunt differentiatingcircuit interposed in the coupling between said variable ratiotransformer secondary winding and the control electrode means, andterminals for connecting a direct-current device to be controlled inseries with said anode-cathode circuit.

UNITED STATES PATENTS References Cited in the file of this patent993,843 Kruh May 30, 1911 1,809,625 Griggs June 9, 1931

